I. Internal factors
The increase in crop yields and other desirable characters are related to Genetic make up of plants.
• High yielding ability
• Early maturity
• Resistance to lodging
• Drought flood and salinity tolerance
• Tolerance to insect pests and diseases
• Chemical composition of grains (oil content, protein content )
• Quality of grains (fineness, coarseness)
• Quality of straw (sweetness, juiciness)
The above characters are less influenced by environmental factors since they are governed by
genetic make-up of crop.
2. External factors
A. CLIMATIC FACTORS
Nearly 50 % of yield is attributed to the influence of climatic factors.The following are the
atmospheric weather variables which influences the crop production.
3. Atmospheric humidity
4. Solar radiation
5. Wind velocity
6. Atmospheric gases
• Precipitation includes all water which falls from atmosphere such as rainfall, snow, hail, fog
• Rainfall one of the most important factor influences the vegetation of a place.
• Total precipitation in amount and distribution greatly affects the choice of a cultivated species
in a place.
• In heavy and evenly distributed rainfall areas, crops like rice in plains and tea, coffee and
rubber in Western Ghats are grown.
• Low and uneven distribution of rainfall is common in dryland farming where drought resistance
crops like pearl millet, sorghum and minor millets are grown.
• In desert areas grasses and shrubs are common where hot desert climate exists
• Though the rainfall has major influence on yield of crops, yields are not always directly
proportional to the amount of Precipitation as excess above optimum reduces the yields
• Distribution of rainfall is more important than total rainfall to have longer growing period
especially in drylands
• Temperature is a measure of intensity of heat energy. The range of temperature for maximum
growth of most of the agricultural plants is between 15 and 40ºC.
• The temperature of a place is largely determined by its distance from the equator (latitude) and
• It influences distribution of crop plants and vegetation.
• Germination, growth and development of crops are highly influenced by temperature.
• Affects leaf production, expansion and flowering.
• Physical and chemical processes within the plants are governed by air temperature.
• Diffusion rates of gases and liquids changes with temperature.
• Solubility of different substances in plant is dependent on temperature.
• The minimum, maximum (above which crop growth ceases) and optimum temperature of
individual’s plant is called as cardinal temperature.
Crops Minimum Optimum Maximum
temp. ºC temp. ºC temp. ºC
Rice 10 32 36-38
wheat 4.5 20 30-32
Maize 8-10 20 40-43
Sorghum 12-13 25 40
Tobacco 12-14 29 35